This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Specific Aims The overall objective of our work is to determine whether chemoprevention can prevent cancer in humans. Oral leukoplakia (OL) is an easily assessable, clinically identifiable precursor to head and neck cancer represents an excellent model system in which to study chemoprevention, and one with which the investigators are familiar. Both epidemiologic and experimental data strongly suggest a broad role for protease inhibitors in providing a protective effect against cancer formation. Preclinical toxicology studies indicate that these agents are remarkably free of side effects and safe. The investigators have conducted an FDA-required phase I trial of the soybean-derived Bowman-Birk Inhibitor Concentrate (BBIC) as the prototype agent and have been approved to do longer term studies. The effect of BBIC on buccal mucosa cells (BMC) will be investigated with respect to the following intermediate marker endpoints (IME): 1) clinical and histologic status of leukoplakia, 2) level of proteolytic activity (PA) using the protease substrates Boc-Val-Pro-Arg-MCA and GH-Gly-Arg-MCA, and 3) level of RNA expression (c-erb-B). These studies will be performed in the context of two sequential clinical chemoprevention trials.